Process for preparing polymeric polyamides



Patented Aug. 11, 1942 PROCESS FOR PREPARING POLYMERIC POLYAMIDESWilliam E. flanford, Wilmington, DeL', assignor to E. I. du Pont deNemours & Company, Wilmington, Del., a corporation of Delaware NoDrawing. Application July 17, 1940,

Serial N- 346,038

10 Claims.

This invention relates to polymeric materials, and more particularly toa new process for making linear carbamide polymers.

Common subject matter appears in applicant's application Serial No.232,469, filed September 29, 1938.

Polymethylcne carbamide has been prepared.

by heating a mixture of tetramethylene diamine and carbon dioxide in aclosed vessel. Carbamide polymers of high molecular weight havingfiber-forming properties are included with other linear polyamides ofthese properties obtained from diamines and dibasic carboxylic acidsdisclosed in Patents 2,071,250 and 2,130,948. The present invention isparticularly concerned with the manufacture of the fiber-formingcarbamide polymers from reactants not heretofore used in the manufactureof polyamides.

An object of this invention is to provide a new and improved process forthe preparation of linear carbamide polymers. A further object is toprepare linear carbamide polymers which can be utilized in themanufacture of synthetic fibers. Other objects will appear hereinafter.

;These objects are accomplished by reacting, in

substantially equimolecular proportions, a diisocyanate of the generalformula OCNR,NCO with a diamine of the general formula R"NH,R'--NHR"wherein R and R are divalent organic radicals in which the terminalatoms are carbon and R." and R are hydrogen or monovalent hydrocarbonradicals, until a polymer of the desired properties is prepared.

Substantially equimolecular quantities of a diamine and a diisocyanateare reacted at polymerizing temperatures, generally between 50 and 250C., until a polymer of the desired properties (degree of polymerization)is attained. By substantially equimolecular quantities is meant not morethan 5% molar excess of either reactant. In its preferred embodiment thereaction is continued until the product exhibits fiber-formingproperties. Generally the polymeric carbamides do not exhibitfiber-forming properties until their intrinsic viscosity (as defined inthe above mentioned Patent 2,130,948) is at least 0.2.

It is preferable to operate in a medium which dissolves the polymer. aswell as the reactants. Although the presence of such a solvent is by nomeans necessary, its use permits formation of a homogeneous reactionmixture at atemperature substantially lower than that necessary if thereactants were melted together. i

The reaction involved may be represented as follows? I wherein R and Rare divalent organic radicals which may be identical or different.Neither R nor R should have attached any functional groups, other thanthose indicated in the above equation, which would react under theconditions of polymerization with the isocyanate groups or the aminegroups. Preferably R and R are hydrocarbons. It is to be observed thatpolymeric carbamides cannot'be obtained by reaction between a monoamineand an isocyanate.

The invention is illustrated by the following examples in which thequantities of reagents are given in parts by weight:

Example I Decamethylene diisocyanate is prepared by dissolving 86 partsof decamethylenediamine in 1155 parts of warm xylene to which is added36.5 parts of dry hydrogen chloride. The suspension ofdecamethylencdiamine dihydrochloride is heated to boiling, a smalladditional amount of hydrogen chloride is added, and the suspension isheated at reflux while a slow stream of dry phosgene is passed into theliquid. When most of the solid is dissolved the solution is filtered,the xylene removed from under reduced pressure and the remainderdistilled twice, giving parts of decamethylene diisocyanate boiling at151-153" C. at 3 mm. pressure.

To a solution of 19 parts of decamethylenediamine in 39 parts ofm-cresol is added 24.7 parts of dccamethylene diisocyanate. Aprecipitate forms at once with considerable evolution of heat. Themixture is then heated at 218 C. whereupon the precipitate dissolves andthe clear solution soon becomes viscous. After 5 hours at 218 C. thesolution is poured into a large volume of ethanol. The polymer,polydecamethylene carbamide, separates as a white solid which is thenthoroughly washed with ethanol. Its melting 'point is 209-210 C. It isreadily spinnable to long filaments capable of being cold drawn intoExample [I To a solution of 17 parts of decamethylene diamine in 45parts of ethanol is added 22 parts of decamethylene dii'socyanate. Heatis evolved and a white solid separates. The polymeric carbamide soobtained melts to a clear, viscous melt' and is capable of being drawninto filaments.

Example III To a solution of.'7.9 parts of hexamethylenediamine in- 15cc. of m-cresolis added 11.4 parts of hexamethylene diisocyanate (B. P.ill-112 C./4 mm.). A precipitate forms immediately with evolution ofmuch heat. On heating the mixture the precipitate all dissolves and aclear solution is obtained. This solution is heated at 205-2l0 C. forseven hours, then diluted with alcohol, whereupon the polymericcarbamide precipitates as a light gray solid. After thorough washingwith alcohol, the polymer melts at 2692'70 C. It can be spun intofilaments which can be cold drawn.

Example IV A mixture of 39.7 parts of m-phenylene diisocyanate (M. P.5051 C.) and 26.8 parts of m-phenylene diamine is heated in anatmosphere of oxygen-free nitrogen at 140 C. for 30 minutes, then at 180C. for 4 hours. The mixture is incompletely fused at this temperature;'

even at 340 C. a portion of the product remains solid. The polymer is aglassy solid, capable of being drawn into filaments.

Example V A solution of 8.4 parts of hexamethylene diisocyanate in partsof dimethylformamide is added to a solution of 7.8 parts ofp-xylylenediamine in 10 parts of dimethylformamide. An additional 200parts of the solvent is added and the white solid which forms is brokenup and heated in a solvent for onehalf hour. At the end of this time thewhite solid is collected on a filter'and is dried. It is insoluble inethyl alcohol and melts with decomposition above 305 C.

Example VI A solution of 8.4 parts of hexamethylene diisocyan ate in 50parts of dimethylformamide is added to a solution of 8.2 parts ofN,N'-dimethylxylylene diamlne in 50 parts of the same solvent. The clearsolution which results is heated at gentle refluxing temperature for onehour. The solution is poured into 500 parts of ethyl alcohol. on coolinga white precipitate forms and this is collected on a filter and isdried. v

The final product was a brittle solid having a softening point of 80 C.and capable of being spun into fibers.

- Examples of other diisocyanates that may replace those given in theexamples are as follows: Polymethylene diisocyanates, such as ethylenediisocyanate, trimethylene diisocyanate, and hexadecamethylenediisocyanate; alkylene diisocyanates such as propylene-1,2-diisocyanate,butylene-l,2-diisocyanate, butylene-l,3-diisocyanate, andbutylene-2,3-diisocyanate; alkylidene diisocyanates such as ethylidenediisocyanate,

carrying a functional group or groups, other than the two isocyanategroups, which will react with an isocyanate group or' an amino groupunder the conditions of polymer formation, will react with a widevariety of diamines to give polymeric carbamides. For example adiisocyanate such as (OCNCH2CI-IzCH2O)2 or its sulfur analog isoperable. The preferred diisocyanates, however, are those in which theisocyanate groups are separated by a hydrocarbon radical containing achain of at least 4 carbon atoms between the isocyanate groups. A largenumber of diamines may be used in place of those mentioned in theexamples, as for instance polymethylene, alkylene, cycloalkylene,aromatic and aliphatic-aromatic diamines, primary or secondary. Asparticular examples of other diamines, there may be mentionedethylenediamine, trimethylenediamine, tetramethylenediamine,octamethylenediamine, dodecamethylenediamine,

' N,N'-dimethylhexamethylenediamine, N,N-dimethyldecamethylenediamine,N,N-dibenzylhex-- amethylenediamine, cyclohexylene-1,4-diamine,o-phenylenediamine, p-phenylenediamine, benzidine,naphthylene-1,4-diamine, -y,-y'-diaminodibutyl oxide, fl-diaminodibutylsulfide, etc. The

preferred diamines are diprimary diamines in which the amino groups areseparated by a hy drocarbon radical containing a chain of at least 4carbon atoms between the amino groups.

The polymerization may be conducted either in the presence or absence ofsolvents or diluents and at atmospheric, superatmospheric orsubatmospheric pressures. The reaction is preferably conducted in theabsence of oxygen or moisture, which may be accomplished either byoperating in a partial vacuum or in the presence of an inert gas such asnitrogen. In some cases the reaction proceeds at ordinary temperaturesbut in most cases it is desirable to operate at temperatures notsubstantially below C. This reaction does not require a high temperatureand in general it is advantageous to operate below 250 C. Modifyingagents, such as plasticizers or delusterants, may be incorporated withthe reaction mixture provided they do not react with the functionalgroups.

The polymer may be freed of solvent by direct .distillation of thesolvent under reduced pressure,

or the polymer may be precipitated by the addition of a solvent in whichit. is insoluble, such as methanol, ethanol, acetone, or ethyl acetate.It

may be advantageous in some cases to operate in a medium in which thepolymer is insoluble and from which it separates as soon as it forms.

In the preferred embodiment of this invention the reactants are heateduntil the resulting polymer exhibits fiber-forming properties. Thisstage is readily determined by touching the molten polymer with a glassrod and drawing the rod quickly away. If the fiber-forming stage isreached a filament of considerable strength and pliability will beformed which is capable of being cold drawn, that is drawn byapplication of tensile stress below its melting point, into fibers whichexhibit upon X-ray examination molecular orientation along thefiber-axis. This process, however, is not limited to the manufacture ofth" fiber-forming polymers and it is within the scope of this inventionto discontinue heating before that stage is reached. The low molecularweight as viscosity stabilizing agent a small amount of prepareinterpolymers' by reacting two or more different diamines with a singlediisocyanate, or conversely two or more different diisocyanates with asingle diamine.

. The polymeric carbamides are colorless or light-colored solids of highmelting points. They are insoluble in the common solvents but may bedissolved in certain solvents such as m-cresol, nitrobenzene or formicacid. This property per-.

mits spinning from solutions whenever the melt-- ing point of thepolymeric carbamide is too high to allow spinning from the melt. Thefilaments may be cold drawn to highly oriented fibers.

The polymeric carbamides obtained by the present process are generallyuseful for the purposes mentioned in connection with the polyamidesdescribed in the above mentioned patents. The more important of theseuses are the production of continuous oriented filaments suitable tobeused as artificial silk, artificial hair, bristles,

threads, ribbons, etc. The polymeric carbamides are also of value ascoating agents for cloth, paper, leather, etc. Furthermore, they ar:well adapted for use in the manufacture of safety glass interlayerssince they are capable of being molded into clear, tough sheets adheringtenaciously to glass.

In these and other uses the polymeric carbamides may be admixed withother polymers,

resins, plasticizers, pigments, dyes, etc.

The new process described herein permits the preparation of linearpolymers with a wide range of molecular weight. further advantageous inthat it does not require such high temperatures as most superpolymericreactions and since there is no evolution of byproducts can be carriedout without difficulty in closed vessels.

As many apparently widely different embodiments of this invention may bemade without departing from the spirit and scope thereof, it is to beunderstood that I do not limit myself to 'the specific embodimentsthereof except as defined in the appended claims.

I claim: 1

The present invention iscyanate of the general formula OCN-Rr-NCO with adiamine ofthe general formula R 'NHRNHR' wherein Rand R. are divalentorganic radicals in which the terminal atoms are carbon, and R" and Rare constituents of the class consisting of hydrogen and monovalenthydrocarbon radicals. L

2. A process which comprises heating to reaction temperaturesubstantially equimolecular quantities of a diisocyanate of the generalformula OCN-R-NCO and a diamine of the general formula R"NHR'NI-IR"'wherein R and R are divalent organic radicals in which the terminalatoms are carbon, and R" and R' are constituents of the class consistingof hydrogen and monovalent hydrocarbon radicals, and continuingthereaction until a fiber-forming polymeric carbamideis obtained.

3. A process formaking polymeric carbamides which comprises heating toreaction temperature a solution in organic solvent ofsubstantiallyequimolecular quantities of a diisocyanate of the general formulaOCN'RNCO with a diamine of the general formula R. 'NH--R'-NHR' wherein Rand R'are divalent organic radicals in which the terminal atoms arecarbon, and R." and R are constituents of the class consisting ofhydrogen and monovalent hydrocarbon radicals.

4. A process which comprises heating to reaction temperature in thepresence of a viscosity stabilizing agent substantially J equimolecularquantities of a diisocyanate of the general formula OCN-Rr- NCO and adiamine of the general formula R"NHR'NHR"' wherein R and R are divalentorganic radicals in which the 1 terminal atoms are carbon, and R." andR".are constituents of the class consisting of hydrogen and monovalenthydrocarbon radicals, and'con-' tinuing the reaction until afiber-forming polymeric carbamide is obtained, said agent being selectedfrom the class consisting of monoamines,

1. A process for making polymeric carbamides which comprises heating toreaction temperature diamines, monoisocyanates, diisocyanates, monobasicacids, and dibasic acids.

5. The process set forth inclaim 2 in which said temperature is between50 C and 200 C.

6. The. process set forth in claim 1 in which said diisocyanate ishexamethylene diisocyanate.

7. The process set forth in claim 1 in which said diisocyanate isdecamethylene diisocyanate.

8. The process set forth in claim 1 in which said diamine isdecamethylene diamine.

9. The process set forth in claim 1 in which said diamine ishexamethylene diamine.

10. A process for making polymeric carbamides which comprises heating toreaction @mperature decamethylene diisocyanate with decamethylenediamine.

WILLIAM E. HANFORD.

